Liquid crystal display device

ABSTRACT

A liquid crystal display device in which smear error is suppressed and transmittance is uniform is provided. 
     In a liquid crystal display device which includes a plurality of pixels and uses comb-teeth-shaped transparent conductive films  110  as common wirings, the common wirings include mesh-shaped common metal wirings  101   v  and  101   h  extending in a vertical direction and a horizontal direction and the comb-teeth-shaped transparent conductive films  110  are connected between adjacent pixels.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2013-230507 filed on Nov. 6, 2013 the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device and amanufacturing method thereof.

BACKGROUND ART

In a large screen and high resolution monitor product (the number ofpixels is about 10 M/30 inches) for broadcasting and medicalapplications, wiring length becomes long and wiring resistance becomeshigh, so that smear error often occurs. This tendency is also seen in aC-Top IPS (In-Plane Switching) type liquid crystal display device inwhich common wiring formed by a transparent conductive film (ITO) isarranged at an upper area of pixel electrode, so that a countermeasureagainst, smear is performed by additionally creating horizontal commonmetal wiring having the same potential as that of the common ITO inorder to reduce common resistance, in particular, in the horizontaldirection in which the device size is large. FIG. 1A illustrates aschematic plan view of a partial configuration of a display area of theliquid crystal display device. Drain lines 105 that are video signallines are arranged in the vertical direction. An area surrounded by thedrain lines 105 and scanning signal lines arranged in the horizontaldirection forms a pixel. A large number of common ITO wirings 110 arearranged in a pixel area. A horizontal common metal wiring 101 h isarranged in an area (horizontal direction) overlapping the scanningsignal line (gate wiring). The liquid crystal display device isdisclosed in, for example, Japanese Unexamined Patent ApplicationPublication No. 2009-150952

SUMMARY OF THE INVENTION Technical Problem

Liquid crystal display devices for monitor products tend to have alarger screen and higher resolution. Therefore, a trial product of aliquid crystal display device having a much larger screen ismanufactured, and then it is found that a countermeasure of only addinghorizontal common metal wirings is not sufficient to prevent the smearerror. To further reduce the common wiring resistance, the inventorsexamined a structure in which vertical common metal wirings having thesame potential as that of the common ITO are added to the horizontalcommon metal wirings and the horizontal common metal wirings and thevertical common metal wirings are arranged in a mesh pattern. FIG. 1Billustrates a schematic plan view of a partial configuration of adisplay area of this liquid crystal display device. A vertical commonmetal wiring 101 v is arranged in an area overlapping the drain line105, which is a video signal line. When the metal wirings are arrangedin a mesh pattern in the vertical and horizontal directions, the commonresistance in the vertical direction can be reduced by about 10% and thesmear error is suppressed. However, it is found that the appearance ofdomain areas (non-transparent areas) changes while being driven and thetransmittance changes.

An object of the present invention is to provide a liquid crystaldisplay device in which the smear error is suppressed and thetransmittance is uniform.

Solution to Problem

As an embodiment to achieve the above object, in a liquid crystaldisplay device which includes a plurality of pixels and usescomb-teeth-shaped transparent conductive films as common wirings,

the common wirings include mesh-shaped common metal wirings extending ina vertical direction and a horizontal direction, and

the comb-teeth-shaped transparent conductive films are connected betweenadjacent pixels.

Further, in a liquid crystal display device which includes a pluralityof pixels and pluralities of video signal lines and scanning signallines, each o which is connected to the plurality of pixels, and usescomb-teeth-shaped transparent conductive films as common wirings,

the common wirings include mesh-shaped common metal wirings extending ina direction along the video signal lines and a direction along thescanning signal lines, and

the comb-teeth-shaped transparent conductive films are connected.between pixels adjacent to each other with the video signal line inbetween.

Further, in a liquid crystal display device which includes a pluralityof pixels and pluralities of video signal lines and scanning signallines, each of which is connected to the plurality of pixels, and usescomb-teeth-shaped transparent conductive films as common wirings,

the common wirings include mesh-shaped common metal wirings extending ina direction along the video signal lines and a direction along thescanning signal lines, and

the comb-teeth-shaped transparent conductive films are connected betweenpixels adjacent to each other with the scanning signal line in between.

Advantageous Effect of the Invention

According to the present invention, it is possible to provide a liquidcrystal display device in which the smear error is suppressed and thetransmittance is uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view of a main part (pixel portion includingcommon wirings) of a display area of a conventional liquid crystaldisplay device.

FIG. 1B is a plan view of a main part (common wirings) of a liquidcrystal display device examined by the inventors.

FIG. 2A is a process flow of a main manufacturing process of a pixelportion of a liquid crystal display device according to embodiments,which is examined by the inventors.

FIG. 2B is a process flow diagram of common wirings (in a state in whichcommon metal wirings are formed) of a liquid crystal display deviceaccording to a first embodiment, which is examined by the inventors. Anupper diagram is a plan view and a lower diagram is a cross-sectionalview taken along a line A-A′ in the upper diagram.

FIG. 2C is a process flow diagram of common wirings (in a state in whichcommon ITO wirings are formed) of the liquid crystal display deviceaccording to the first embodiment, which is examined by the inventors.An upper diagram is a plan view and a lower diagram is a cross-sectionalview taken along a line B-B′ in the upper diagram.

FIG. 3A is a plan view of a main part (common wirings) of the liquidcrystal display device examined by the inventors and an enlarged planview of a vertical common wiring portion.

FIG. 3B is plan views of the common wiring of the liquid crystal displaydevice examined by the inventors. An upper diagram illustrates a case inwhich a comb tooth tip is formed by ITO+metal and a lower diagramillustrates a case in which a comb tooth tip is formed by only ITO.

FIG. 4 is a plan view of common wirings of a liquid crystal displaydevice according to the first embodiment of the present invention.

FIG. 5A is a plan view of a pixel portion of a liquid crystal displaydevice (normal comb-teeth-shaped common ITO wirings) includingmesh-shaped common metal wirings examined by the inventors.

FIG. 5B is a plan view of a pixel portion of a liquid crystal displaydevice according to a second embodiment of the present invention.

FIG. 5C is a plan view of a pixel portion of a liquid crystal displaydevice according to a third embodiment of the present invention.

FIG. 6 is an example of a conventional monitor product and a monitorproduct according to the embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors examined a cause of the change of appearance of the domainareas (non-transparent areas) when being driven. FIG. 2A (1) illustratesa process flow of a main manufacturing process of a pixel area examinedby the inventors. By the processes 1 to 3, a switching thin filmtransistor (TFT) formed in the pixel area and a drain line connected tothe drain of the TFT are formed. Subsequently, an inorganic passivation(PAS) film (process 4) and an organic passivation film are formed(process 5), and then a pixel electrode (CIT) connected to the source ofthe TFT is formed (process 6). Subsequently, an upper inorganicpassivation film (UPS) is formed (process 7). Thereafter, a common metallayer and a common ITO are formed (processes 8 and 9). It is consideredthat the horizontal common metal wirings are time-proven and highlyreliable, so that attention is paid to the vertical common metal wiringsin particular.

FIGS. 3A and 3B illustrate a plan view of a main part (common wirings)of a liquid crystal display device examined by the inventors. An area inwhich a vertical area denoted by reference numeral 140 and a horizontalarea denoted by reference numeral 140 cross each other is a pixel area.A vertical common metal wiring 101 v is arranged in an area overlappingthe drain line 105, which is a video signal line. FIG. 3. illustrates acase in which the appearance of the domain area (non-transparent area)varies.

As a result of this examination, it is found that the comb tooth tip isformed by ITO+metal in the upper diagram in FIG. 3B, but the comb toothtip is formed by only ITO in the lower diagram in FIG. 38. Therefore,the above difference is further examined. As a result, it is found thatthe position, thickness, length, and tip shape of comb of the comb toothvary due to unevenness (variation of etching conditions, variation ofpositioning, and the like) of processing of a common ITO film, so thatthat is a case in which the common. ITO reaches the vertical commonmetal wiring 101 v and a case in which the common ITO does not reach thevertical common metal wiring 101 v. The present invention is made by thenew knowledge described above, and in the present invention, the combtooth of the common ITO wiring is extended and connected between pixelsadjacent to each other. Thereby, the comb tooth tip disappears, so thateven if the processing is uneven, the positional relationship betweenthe comb tooth tip and the common metal does not change. Therefore, thecomb tooth tip is stably formed by ITO metal. Thereby, it is possible toachieve uniform transmittance while suppressing smear error.Hereinafter, the present invention will be described using embodiments.The same reference numerals indicate the same components.

FIRST EMBODIMENT

A first embodiment of the present invention will be described withreference to FIGS. 2A to 2C and 4. Facts that are not described in thepresent embodiment among results of the examination of the inventorsdescribed above can be applied to the present embodiment unless thereare special circumstances. FIG. 2A (1) is a process flow of a mainmanufacturing process of a pixel portion of a liquid crystal displaydevice (C-Top IPS type) according to the present embodiment. Amanufacturing method will be described with reference to FIG. 2A (1).

<Process 1: Form Gate>

First, a gate electrode is formed on a TFT substrate formed of glass.The gate electrode is formed in the same layer as that of a scanningsignal line. A laminate in which a Mo alloy is laminated on an Al alloyis used for the gate electrode. However it is not limited to this. Next,an insulating film is formed from SiN. A portion of the insulating film,which covers the gate electrode, is a gate insulating film.

<Process 2: Form a-Si>

Subsequently, a semiconductor layer is formed at a position facing thegate electrode with the gate insulating film in between. In the presentembodiment, as the semiconductor layer, an a-Si film is formed by plasmaCVD. The semiconductor layer forms a channel portion of the TFT.

<Process 3: Form Drain/Source>

Subsequently, a source electrode and a drain electrode are formed on thesemiconductor layer with the channel portion in between. An n+Si layeris formed between the semiconductor layer and the drain electrode or thesource electrode. This is to form an ohmic contact between thesemiconductor layer and the drain electrode or the source electrode. Thedrain electrode is also used as a video signal line. The sourceelectrode and the drain electrode are formed in the same layer at thesame time. In the present embodiment, the source electrode or the drainelectrode is formed from a Mo alloy. When it is desired to reduce theelectrical resistance of the source electrode or the drain electrode,for example, an electrode structure in which an Al alloy is sandwichedby Mo alloys may be used. The names such as source and drain are forconvenience, and when one is termed as the source, the other can becalled the drain.

<Process 4: Form PAS>

Subsequently, an inorganic passivation (PAS) film is formed from SiN tocover the TFT. The PAS film protects, in particular, the channel portionof the TFT from impurities.

<Process 5: Form Organic PAS>

Subsequently, an organic PAS film is formed on the PAS film and anopening from which the source electrode is exposed is formed in alaminated film of the PAS film and the organic PAS film.

<Process 6: CIT (Form Pixel Electrode)>

Subsequently, ITO (Indium Tin Oxide), which is a pixel electrode, isformed by sputtering to cover the laminated film of the PAS film and theorganic PAS film which includes the opening from which the sourceelectrode is exposed. The pixel electrode is formed to have a planarshape.

<Process 7: Form UPS>

Subsequently, an upper inorganic passivation (UPS) film is formed fromSiN to cover the pixel electrode.

<Process 8: Form Common Metal>

Subsequently, a common metal film 101 v is formed, coated with aphotoresist film, exposed, and developed, and then the common metal filmis processed. FIG. 2A illustrates a plan view of this state and across-sectional view taken along a line A-A′ in the plan view. Referencenumeral 105 denotes a drain line and reference numerals 120 and 121denote an insulating film (PAS film, UPS film, and the like).

<Process 9: Form Common ITO>

Subsequently, ITO (Indium Tin Oxide), which is a transparent conductivefilm, is formed on the entire display area by sputtering and common ITOwirings are formed by patterning the sputtered ITO. The common ITOwirings have a comb-teeth-shaped electrode structure. FIG. 2Cillustrates a plan view this state and a cross-sectional view takenalong a line B-B′ in the plan view, and FIG. 4 illustrates an enlargedview of the plan view. A common metal wiring 101 v is connected to acommon ITO wiring 110 (FIG. 2C) and their potentials are the same. Asillustrated in FIG. 4, the comb-teeth-shaped common ITO wirings areconnected between horizontally adjacent pixels (between pixels adjacentto each other with a vertical common metal wiring in between) and a combtooth tip (pixel end portion) is formed from ITO+metal. By employingthis configuration, the tip shape of the comb tooth can be stably formedeven if the size and the position of the common wirings vary. Thereby,the domain areas (non-transparent areas) become stable, so that thetransmittance becomes stable.

In the present embodiment, a part of upper surface and one side surfaceof the common metal wiring are covered by the common ITO wiring.However, the upper surface and both side surfaces of the common metalwiring may be covered by the common ITO wiring. The liquid crystaldisplay device according to the present embodiment can be manufacturedby the process flow illustrated in FIG. 2A (2) in this process flow, thecommon ITO wiring is formed in the process 8, and the common metalwiring is formed in the process 9.

Thereafter, the liquid crystal display device is formed by attachingtogether a counter substrate in which a color filter and a black matrixare formed and the aforementioned TFT substrate with a liquid crystal inbetween.

When the liquid crystal display device is applied to a display unit 150of a monitor product illustrated in FIG. 6, occurrence of the smearerror can be reduced or prevented. Reference numeral 160 denotes aframe.

As described above, according to the present embodiment, the commonwirings are formed by the common ITO wirings and the mesh-shaped commonmetal wirings, and the comb-teeth-shaped common ITO wirings areconnected between adjacent pixels, so that it is possible to provide aliquid crystal display device in which the smear error is suppressed andthe transmittance is uniform.

SECOND EMBODIMENT

As illustrated in FIG. 5A, a liquid crystal display device includingnormal comb-teeth-shaped common ITO wirings Forms a dual domain in onepixel, which is an area where a vertical area denoted by referencenumeral 140 and a horizontal area denoted by reference numeral 140 crosseach other, for a countermeasure against color shift. Therefore, adomain area (non-transparent area: light shielding area) 130 is formedat a central portion of a pixel. The domain area is formed by quick turnof the comb teeth at the central portion of the pixel and causes adomain loss. A second embodiment including avoidance of the domain losswill be described with reference to FIG. 5B. Matters which are describedin the first embodiment but not described in the present embodiment canbe applied to the present embodiment unless there are specialcircumstances.

FIG. 5B is a plan view of a pixel portion of a liquid crystal displaydevice according to the present embodiment and illustrates horizontalmulti-domain pixels. The structure illustrated in FIG. 5B may bereferred to as a pseudo dual domain structure or a pseudo multi-domainstructure. In the present horizontal multi-domain pixel, regarding thecommon ITO wirings extending slightly obliquely upward and the commonITO wirings extending slightly obliquely downward, which are so fararranged in one pixel, one set of wirings is arranged in one pixel andthe other set of wirings is arranged in a pixel immediately below(above) the one pixel, so that a pseudo dual pixel is formed by usingtwo pixels. When the size of the pixels is reduced, it is possible toreduce color shift in combination with an adjacent pixel. Also in thepresent configuration, the comb-teeth-shaped common ITO wirings areconnected between horizontally adjacent pixels (between pixels adjacentto each other with a vertical common metal wiring in between) and a combtooth tip is formed in combination with a vertical common metal wiring.As the horizontally adjacent pixels, there are a combination of a redpixel and a green pixel, a combination of a green pixel and a bluepixel, and a combination of a blue pixel and a red pixel. In the presentconfiguration, there is no domain area (non-transparent area) in onepixel, so that it is possible to prevent the domain loss.

When the common metal wirings are formed on the common ITO wiringsaccording to the process flow illustrated in FIG. 2A (2) and a liquidcrystal display device having the configuration illustrated in FIG. 5Bis manufactured and applied to the display unit 150 of the monitorproduct. illustrated in FIG. 6, there is no domain loss, and occurrenceof the smear error can be reduced or prevented. Reference numeral 160denotes a frame.

As described above, according to the present embodiment, the commonwirings are formed by the common ITO wirings and the mesh-shaped commonmetal wirings, and the comb-teeth-shaped common ITO wirings areconnected between adjacent pixels, so that it is possible to provide aliquid crystal display device in which the smear error is suppressed andthe transmittance is uniform. Further, it is possible to prevent thedomain loss by employing the horizontal multi-domain pixels.

THIRD EMBODIMENT

A third embodiment of the present invention will be described withreference to FIG. 5C. Matters which are described in the first and/orthe second embodiments but not described in the present embodiment canbe applied to the present embodiment unless there are specialcircumstances. In the first and the second embodiments, the extendingdirection of the comb teeth is approximately horizontal. However, in thepresent embodiment, a case in which the extending direction of the combteeth is approximately vertical will be described.

FIG. 5C is a plan view of a pixel portion of a liquid crystal displaydevice according to the present embodiment and illustrates verticalmulti-domain pixels. The structure illustrated in FIG. 5C may bereferred to as a pseudo dual domain structure or a pseudo multi-domainstructure. In the present vertical multi-domain pixel, regarding thecommon ITO wirings extending obliquely upward and the common ITO wiringsextending obliquely downward, which are so far arranged in one pixel,one set of wirings is arranged in one pixel and the other set of wiringsis arranged in a pixel immediately below (above) the one pixel, so thata pseudo dual pixel is formed by using two pixels. Also in the presentconfiguration, the comb-teeth-shaped common ITO wirings are connectedbetween vertically adjacent pixels (between pixels adjacent to eachother with a horizontal common metal wiring in between) and a comb toothtip is formed in combination with a horizontal common metal wiring. Asthe vertically adjacent pixels, there are a combination of a red pixeland a red pixel, a combination of a green pixel and a green pixel, and acombination of a blue pixel and a blue pixel. In the presentconfiguration, there is no domain area (non-transparent area) in onepixel, so that it is possible to prevent the domain loss.

When the common metal wirings are formed on the common ITO wiringsaccording to the process flow illustrated in FIG. 2A (2) and a liquidcrystal display device having the configuration illustrated in FIG. 5Cis manufactured and applied to the display unit 150 of the monitorproduct illustrated in FIG. 6, there is no domain loss, and occurrenceof the smear error can be reduced or prevented. Reference numeral 160denotes a frame.

As described above, according to the present embodiment, the commonwirings are formed by the common ITO wirings and the mesh-shaped commonmetal wirings, and the comb-teeth-shaped common ITO wirings areconnected between adjacent pixels, so that it is possible to provide aliquid crystal display device in which the smear error is suppressed andthe transmittance is uniform. Further, it is possible to prevent thedomain loss by employing the vertical multi-domain pixels.

The present invention is not limited to the embodiments described above,but various modified examples are included in the present invention. Forexample, the above embodiments are described in detail in order toexplain the present invention in an easily understandable manner and arenot necessarily limited to devices that include all the componentsdescribed above. Further, a part of components of a certain embodimentcan be replaced with components of another embodiment, and components ofa certain embodiment can be added to components of another embodiment.It is possible to perform addition/deletion/replacement of othercomponents on a part of components of each embodiment.

What is claimed is:
 1. A display device comprising: a display areaperforming a display of an image; a plurality of pixels arranged in theform of a matrix in the display area; scanning signal lines and videosignal lines in the display area; an insulating film above the scanningsignal lines and the video signal lines; a pixel electrode in thedisplay area; a counter electrode in the display area; and a metalwiring above the insulating film, wherein the metal wiring extends in arow direction of the plurality of pixels or a column direction of theplurality of pixels, and connects to the counter electrode in thedisplay area, and wherein the counter electrode has a plurality of slitswhich are continued for two or more pixels.
 2. The display deviceaccording to claim 1, wherein the two or more pixels are pixels adjacentto each other across the video signal lines.
 3. The display deviceaccording to claim 2, wherein the two or more pixels are pixels of acolor different from each other.
 4. The display device according toclaim 1, wherein the two or more pixels are pixels are pixels adjacentto each other across the scanning signal line.
 5. The display deviceaccording to claim 4, wherein the two or more pixels are pixels of thesame color.
 6. The display device according to claim 1, wherein a dualdomain is formed in each pixel of the plurality of pixels.
 7. Thedisplay device according to claim 1, wherein each of the two or morepixels across a scanning signal line is formed into a pseudo dual pixel.8. The display device according to claim 1, wherein the metal wiringfaces the video signal lines and the width of the metal wiring issmaller than that of the video signal lines.
 9. The display deviceaccording to claim 1, wherein the insulating film is an organic film,and the pixel electrode and the counter electrode are disposed above theorganic insulating film.
 10. The display device according to claim 1,wherein the pixel electrode is disposed above an organic insulatingfilm, and an inorganic insulating film is interposed between the pixelelectrode and the counter electrode.
 11. The display device according toclaim 1, wherein a first area in which the counter electrode and themetal wiring are overlapped and a second area in which a slit of thecounter electrode and the metal wiring are overlapped are formed abovethe video signal lines.
 12. The display device according to claim 1,wherein a first area in which the counter electrode and the metal wiringare overlapped and a second area in which a slit of the counterelectrode and the metal wiring are overlapped are formed above thescanning signal lines.